Waveguide mixer

ABSTRACT

A microwave mixer comprised of crossed waveguides and a crystal mixer. One of the waveguides has input horns at each end which are axially adjustable with respect to the ends of the waveguide. Axial adjustment of a horn with respect to the end of a waveguide varies the width of the gap between the horn and the waveguide to tune the signal input from the horn to the mixer. Accordingly, the mixer may be tuned by adjusting the position of the input horns with respect to the input ports of the mixer.

United States Patent Administration WAVEGUIDE MIXER 12 Claims, 3 DrawingFigs. u.s. Cl .L 325/445, 329/161, 329/162, 332/51 W, 333/73 W, 343/772,1 343/773, 343/786 Int. Cl. H0lp 5/00 Field of Search 325/445, 446;329/161, 162; 332/51 W; 333/73 W; 343/772, 773, 786

References Cited UNITED STATES PATENTS hmp fizr939111-122:1:212, i

Thomas E. Sullivan Watertown;

Lothar Frenlrel, Lynn, both of Mass. 50,207

June 26, 1970 Jan. 4, 1972 The United States of America as representedby the Administrator of the National Aeronautics and Space InventorsAppl. No. Filed Patented Assignee 2,438,521 3/1948 Sharpless PrimaryExaminer-David L. Trafton Attorneys-Herbert E. Farmer and John R.Manning ABSTRACT: A microwave mixer comprised of crossed waveguides anda crystal mixer. One of the waveguides has input horns at each end whichare axially adjustable with respect to the ends of the waveguide. Axialadjustment of a horn with respect to the end of a waveguide varies thewidth of the gap between the horn and the waveguide to tune the signalinput from the horn to the mixer. Accordingly, the mixer may be tuned byadjusting the position of the input horns with respect to the inputports of the mixer.

PATENTEUJAN 41972 Ad hl THOMAS E SULL/ VM/ LOTHAR FREA/KEL Ar/ameyORIGIN OF THE INVENTION The invention described herein was made byemployees of i the United States Government and may be manufactured andBACKGROUND OF THE INVENTION 1. Field ofthe Invention This inventionrelates to the field of waveguide technology and is more particularlydirected to microwave mixers employing crossed waveguide sections.

2. Description of the Prior Art The prior art microwave harmonicmultipliers and mixers generally employ a crossed waveguideconfiguration in which the waveguides share a commonwall at thecrossover junction with a transfer aperture in the central portion ofthe common wall. Microwave energy is supplied to a first of thewaveguides and may be coupled to the second of the waveguides by meansof a crystal mixer. The crystal mixer includes a diode with a cat'swhisker extending from the diode through the transfer aperture into thesecond waveguide. The diode may be any one of several materials e.g.silicon, germanium, steel, nickel. etc.

Efficientrtransfer of the input signal into the mixer is accomplished byforming an integral pyramidal horn inside the input end of the firstwaveguide. A tuning stub is installed in the opposite end of the firstwaveguide and may be adjusted within the opposite endto tune the inputsignal to the mixer. A crossed waveguide device of this type isdisclosed in the article by Bauer et al., Millimeter Wave SemiconductorDiode Detectors, Mixers, and Frequency Multipliers, Proceedings of theIEEE, Volume 54, No. 4, pp. 595, Apr. 1966.

In the crossed waveguide mixers, the number of inputs is limited to oneinput signal per waveguide since the tuning stub blocks the one end ofthe waveguide. If the tuning stub is removed, it is possible to add asecond input signal per waveguide; however, the removal of the stubeliminates the ability to tune the mixer to different input frequencies.

It is accordingly an object .of the present invention to disclose animproved crossed waveguide device which can be employed for mixing morethan two microwave input signals.

It is a further object of the present invention to disclose a crossedwaveguide device in which a plurality of microwave signals can be mixedand each of the signals can be individually tuned for maximum couplingefficiency.

It is a further object of the present invention to disclose a microwavemixing device which is simple in construction and easily tuned toseveral input signals having different frequencies.

SUMMARY OF THE INVENTION The invention relates to a crossed waveguidedevice which can be tuned to several different input signal frequencies.The first waveguide crosses over the second and has an interconnectingtransfer aperture through the common wall of the waveguide at theintersection. Two pyramidal horns are associated with the respectiveends of the first waveguide and are axially adjustable with respect tothe ends so that a tuning cavity between the confronting ends of thehorn and the waveguide can be tuned to the input signals suppliedthrough the horns. In a similar manner, another input may be connectedto one end of the second waveguide so that a third input signal can becombined with inputs from the first waveguide.

Each of the input signal horns connected to the waveguide isindividually supported by a leaf spring which can be flexed with respectto the coupler housing. Displacement of the spring adjusts the tuningcavities between the horns and the respective ends of the waveguides.Fine adjustment of the leaf spring is permitted by a screw whichdisplaces the leaf spring and horns over distances of a few thousandthsof an inch.

BRIEF DESCRIPTION OF THE DRAWINGS The novel microwave mixer will bebetter understood together with its numerous objects and advantages byreference to the followingdrawings wherein the-same elements areidentified by the same reference numeral throughout the several figures.

FIG. 1 is an external'lateral view'of'the waveguide mixer as seen alongthe axis of one of the pyramidal signal input horns.

FIG. 2 is a cross-sectional view of the waveguide mixer taken along theline 2-2 of FIG. 1 and showing the crystal mixer at the intersection ofthe two crossed waveguides.

FIG. 3 is a perspective view of the crossed waveguides in a unitaryform.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 disclose thedetailed structure of the novel crossed waveguide microwave mixer,generally designated 10. While other applications of the mixer arepossible, thepresent invention is described in an embodiment suitablefor use in laser spectroscopy. In this respect, the term laser is usedin reference to any high-frequency electromagnetic source.

The mixer 10 has a structural housing 12 which supports the individualoperating components. The housing 12 is an elongated, conductive memberhaving a hollow central section 14. The housing may be either square orcircular in cross section. At the lower portion of the housing 12 andwithin the hollow central portion 14 are a pair of crossed waveguides l6and 18. While the waveguides 16 and 18 are referred to separately, thetwo waveguides may in actuality be a single, metallic cruciform element,as shown in FIG. 3, constructed by an electroforming process usingprecision mandrels. The material from which the waveguide is formed maybe a conductor, such as brass, and the internal surfaces of thewaveguides may be polished and plated with a high-work function materialsuch as gold.

In FIG. 2 waveguide 16 is shown cut away along a central cross section.Waveguide l8 crosses over waveguide 16at its midpoint where the twowaveguides share a thin common wall. The waveguides l6 and 18 aresupported in the central portion 14 of the housing 12 on a platform 20andare held in position by means ofa clamping block 22. A suitablefastener or bonding agent may be applied between the block 22, thewaveguide 12 and the housing 14 to hole the waveguides in place. Atransfer aperture 24 is drilled through the cruciform structure formingthe crossed waveguides l6 and 18 at the central crossing point of thewaveguides and mating apertures 26 and 28 in the platform 20 in block 22respectively form an open channel through which a crystal mixer,generally designated 30, extends. The crystal mixer is typical of thosefound in the prior art and consists, for example, of a silicon orgermanium crystal 32 and a cats whisker 34 made from a conductivetungsten wire having a point contact with the crystal. The crystal 32 issometimes referred to as a diode due to its semiconductor propertieseven at microwave frequencies.

The crystal mixer 30 is supported in the transfer aperture 24 throughthe crossed waveguides l6 and 18 so that the mixer 30 does not touch thewaveguides 16 and 18. A differential screw assembly 36 having a movablegrip 37 is mounted in the lower end of housing 12 with the grip 37 beingtranslatable vertically toward and away from the waveguides l6 and l8bymeans of a screw drive arrangement (not shown). The purpose of thedifferential screw assembly supporting the crystal diode 32 is toprovide a very fine adjustment in the translational movement of thediode. The crystal 32 is supported on the upwardly projecting end of aconductive supporting block 40 locked within the grip 37 by means of aset screw 42. The one side of the crystal 32 is electrically connectedthrough the screw assembly 36 to the waveguides and housing 12. Thewhisker 34 extends through each of the waveguides and is connected tothe lower end of a conductive post 44 which is held by a force fit inthe insulator 38 in the upper portion of housing 12. The whisker acts asan antenna to abstract electromagnetic energy from the waveguides andtransfer the energy to the crystal 32 for further processing.

At the upper end of housing 12 as seen in FIG. 2, a coaxial connector 39such as a low-frequency-type BNC" or N connector is mounted with acoaxial conductor 41 leading to insulator 38. Within the insulator 38,the conductor 41 is force fitted with conductive post 44 which supportsthe whisker 34. The connector 39 is used to derive the low-frequencyoutput when the waveguide mixer is used with a local oscillator as asuperheterodyne mixer.

A pair of pyramidal signal input horns 50 and 52 are disposed atopposite ends of the waveguide 16. At the inward ends of the horns 50and 52, neck portions 54 and 56 are received respectively in matingrectangular apertures 58 and 60 of the housing 12. The horns 50 and 52and neck portions 54 and 56 are permitted to displace in a generallyaxial direction with respect to the ends of the waveguide 16 by means ofa pair of leaf springs 62 and 64 to which the horns 50 and 52,respectively, are soldered. The leaf springs 62 and 64 are fastened tothe housing 12 at their lower ends by means of bolts 66 and 68. The leafsprings 62 and 64 contain flex hinges 70 and 72, respectively, in thevicinity of the mounting bolts. At the opposite or upper end of thesprings as viewed in FIG. 2, the leaf springs 62 and 64 containapertures through which tuning screws 74 and 76 project respectivelyfrom housing 12. lnterposed between the leaf springs and the tuningscrews are plastic bushings 78 or 80. From this construction, it isreadily apparent that the input horns 50 and 52 can be displacedgenerally in the axial direction with respect to the ends of waveguide16 through the adjustment of the tuning screws 74 and 76. Thisadjustment varies the size ofa gap or tuning cavity formed between theconfronting faces of the horns and end surfaces ofwaveguide 16incrementally from 0, at abutment of the horns with the end surfaces, toa few thousandths of an inch. Such tuning cavities can be employed totransmit microwave energy between the movable waveguides with maximumefficiency.

It will be immediately recognized that the tuning screws areindividually adjustable. As a consequence, electromagnetic radiationintroduced through horn 50 may be of a different frequency than thatintroduced through horn 52, and both inputs can be tuned to the mixerfor maximum efficiency. In the prior art devices, tuning could beaccomplished by adjusting a slug in the end of the waveguide oppositethe signal input horn. However, in the prior art devices, the necessityfor installing a tuning plug in one end of the waveguide eliminated thatend as a receiving port for a second input signal. It will therefore beunderstood that one advantage of the present construction is that twosignal inputs can be transmitted to ports at opposite ends of the samewaveguide and each of the input signals may be individually adjusted formaximum signal transfer.

When the incoming signals in waveguide 16 are combined and transmittedthrough mixer 30 to the whisker 34, it is possible to add a third inputsignal through flange 90 seen in H0. 1, connected to one port on anextended end of waveguide 18. A conventional, adjustable shorting stub92 is mounted to the opposite side of housing 12 from flange 90 andprojects within the end of waveguide 18 for tuning the input signalintroduced at flange 90. In a typical superheterodyne receiver, theflange 90 on waveguide 18 is connected to a local oscillator and thecombined output of the three mixed signals is removed through thelow-frequency connector 39.

While the novel crossed waveguide device has been described in oneparticular embodiment, it is to be understood that various modificationsand substitutions can be made without departing from the spirit of theinvention. While the horns 50 and 52 have been shown mounted on leafsprings, it will be understood that axial translation of the input hornswith respect to the waveguide ends can be acquired by equivalentadjusting mechanisms. At the innermost position, the horns 50 and 52should abut the ends of waveguide 16 and adjustment of the horn by a fewthousandths of an inch permits tuning over a wide spectrum of inputfrequencies. It will therefore be understood that the present inventionhas been described by way of illustration rather than limitation.

What is claimed is:

1. A crossed waveguide device comprising:

a first waveguide having first and second ends;

a second waveguide crossed over and contacting the first waveguide andhaving an interconnecting transfer aperture extending transverselythrough the contacting walls of the waveguides at the crossing;

a first signal horn aligned with first end of the first waveguide; and

first means connected between the first input horn and the firstwaveguide for translating the input horn toward and away from the firstend.

2. The waveguide device of claim 1 including:

a second signal input horn aligned with the second end of the firstwaveguide; and

second means connected between the second input horn and the firstwaveguide for translating the second input horn toward and away from thesecond end.

3. The crossed waveguide device of claim 1 wherein:

the first and second waveguides include apertures in the walls oppositethe contacting walls, the apertures being aligned with theinterconnecting transfer aperture whereby a through passageway is formedat the crossing of the first and second waveguides; and

a crystal mixer composed of a crystal and conductive whisker are mountedin the through passageway in noncontacting relationship with thewaveguides.

4. The crossed waveguide device of claim 3 wherein:

' one side of the crystal is electrically connected to the waveguidesand the whisker contacts the opposite side of the crystal and extends inthe passageway through both of the waveguides in electrically insulatedrelationship with the waveguides.

5. The crossed waveguide device of claim 1 wherein: a housing isprovided for the crossed waveguides, the crossed waveguides beingmounted within the housing; the first signal horn, the housing, and thefirst end of the first waveguide define a tuning cavity between the hornand the waveguide; and

the first means is an adjusting means connected between the first inputhorn and the housing for adjusting the size of the tuning cavity.

6. The crossed waveguide device of claim 5 wherein:

the adjusting means includes a flexible leaf spring connected to thehousing at one portion of the spring and an adjusting screw extendingbetween another portion of the leaf spring and the housing for adjustingthe position of the spring with respect to the housing; and

the first signal input horn is supported adjacent the first end ofthefirst waveguide by the leaf spring.

7. The crossed waveguide device of claim 6 wherein:

the leaf spring of the adjusting means has a first adjusting position inwhich the first signal input horn is supported in abutting relationshipwith the first end of the first waveguide.

8. The crossed waveguide device of claim 7 wherein:

the leaf spring of the adjusting means has a second adjusting positionin which the first signal input horn is displaced incrementally awayfrom the first end of the first waveguide.

9. The crossed waveguide device of claim 2 wherein: a housing isprovided for the crossed waveguides, the crossed waveguides beingmounted within the housing; the housing and the first and second signalhorns define tuning cavities at the respective ends of the firstwaveguide; the first means is first adjusting means connected betweenthe housing and the first signal horn for adjusting the tuning cavity atthe first end of the first waveguide; and

the second means is a second adjusting means connected between thehousing and the second signal horn for adjusting the tuning cavity atthe second end of the first waveguide independently of the cavity at thefirst end.

10. The crossed waveguide device ofclaim 9 wherein:

the first adjusting means has an adjustable screw connection with thehousing for incrementally adjusting the tuning one end; and

an adjustable shorting stub is mounted in the second waveguide at theother end.

12. The crossed waveguide device of claim 9 wherein:

the first and second crossed waveguides are formed by a single metalliccruciform element.

1. A crossed waveguide device comprising: a first waveguide having firstand second ends; a second waveguide crossed over and contacting thefirst waveguide and having an interconnecting transfer apertureextending transversely through the contacting walls of the waveguides atthe crossing; a first signal horn aligned with first end of the firstwaveguide; and first means connected between the first input horn andthe first waveguide for translating the input horn toward and away fromthe first end.
 2. The waveguide device of claim 1 including: a secondsignal input horn aligned with the second end of the first waveguide;and second means connected between the second input horn and the firstwaveguide for translating the second input horn toward and away from thesecond end.
 3. The crossed waveguide device of claim 1 wherein: thefirst and second waveguides include apertures in the walls opposite thecontacting walls, the apertures being aligned with the interconnectingtransfer aperture whereby a through passageway is formed at the crossingof the first and second waveguides; and a crystal mixer composed of acrystal and conductive whisker are mounted in the through passageway innoncontacting relationship with the waveguides.
 4. The crossed waveguidedevice of claim 3 wherein: one side of the crystal is electricallyconnected to the waveguides and the whisker contacts the opposite sideof the crystal and extends in the passageway through both of thewaveguides in electrically insulated relationship with the waveguides.5. The crossed waveguide device of claim 1 wherein: a housing isprovided for the crossed waveguides, the crossed waveguides beingmounted within the housing; the first signal horn, the housing, and thefirst end of the first waveguide define a tuning cavity between the hornand the waveguide; and the first means is an adjusting means connectedbetween the first input horn and the housing for adjusTing the size ofthe tuning cavity.
 6. The crossed waveguide device of claim 5 wherein:the adjusting means includes a flexible leaf spring connected to thehousing at one portion of the spring and an adjusting screw extendingbetween another portion of the leaf spring and the housing for adjustingthe position of the spring with respect to the housing; and the firstsignal input horn is supported adjacent the first end of the firstwaveguide by the leaf spring.
 7. The crossed waveguide device of claim 6wherein: the leaf spring of the adjusting means has a first adjustingposition in which the first signal input horn is supported in abuttingrelationship with the first end of the first waveguide.
 8. The crossedwaveguide device of claim 7 wherein: the leaf spring of the adjustingmeans has a second adjusting position in which the first signal inputhorn is displaced incrementally away from the first end of the firstwaveguide.
 9. The crossed waveguide device of claim 2 wherein: a housingis provided for the crossed waveguides, the crossed waveguides beingmounted within the housing; the housing and the first and second signalhorns define tuning cavities at the respective ends of the firstwaveguide; the first means is first adjusting means connected betweenthe housing and the first signal horn for adjusting the tuning cavity atthe first end of the first waveguide; and the second means is a secondadjusting means connected between the housing and the second signal hornfor adjusting the tuning cavity at the second end of the first waveguideindependently of the cavity at the first end.
 10. The crossed waveguidedevice of claim 9 wherein: the first adjusting means has an adjustablescrew connection with the housing for incrementally adjusting the tuningcavity between the first horn and the first end of the first waveguide;and the second adjusting means also has an adjustable screw connectionwith the housing for incrementally adjusting the tuning cavity betweenthe second horn and the second end of the first waveguide.
 11. Thecrossed waveguide device of claim 9 wherein: a flange connection isjoined to the second waveguide at one end; and an adjustable shortingstub is mounted in the second waveguide at the other end.
 12. Thecrossed waveguide device of claim 9 wherein: the first and secondcrossed waveguides are formed by a single metallic cruciform element.